1. Field of the Invention
The invention is related to a method and a device for producing rolls out of large numbers of flat articles, particularly printed products.
2. Description of Related Art
For the purpose of transportation and intermediate storage, printed products (e.g. intermediate products straight from the printing press) are frequently rolled up in an imbricated formation to form rolls. For other flat articles, which are flexible at least to a limited extent, e.g. for textile articles, such rolls can represent advantageous formations for transport and/or storage.
The rolls as mentioned comprise a substantially cylindrical roll core and at least one winding tape, wherein the winding tape is wound onto the roll core together with the imbricated formation of the flat articles in a tensioned condition and holds the roll together. The end of the winding tape may be closed around the completed roll or fixed in another suitable manner. The winding tape usually has a width, which is significantly smaller than the width of the rolled-up articles. Printed products in most instances are rolled up in an imbricated formation; it is, however, also conceivable to roll the printed products arranged one behind the other, i.e., not overlapping one another.
Rolls as described above and as used in the printing field usually have a diameter of up to more than two meters and may weigh over one ton. The rolled-up products are, for example, approximately 30 to 50 cm wide and imbricated such that the product spacing amounts to around 10 cm or less. Usual winding tapes are approximately 5 to 10 cm wide.
For producing the rolls, winding devices are used comprising the following essential components: means for holding a roll core (usually comprising a horizontal winding axis), means for supplying the imbricated formation of flat articles to a winding point at the periphery of the roll core or of a roll under formation respectively, means for controlled feeding-in of the tensioned winding tape to the winding point and a drive for rotating the roll core or the roll under formation, respectively, at a substantially constant peripheral velocity, the drive acting either on the roll center or at its periphery. Winding devices of this type are described, for example in the publications EP-0243838 (or U.S. Pat. No. 4,775,111), EP-0281790 (or U.S. Pat. No. 4,898,336) or U.S. Pat. No. 4,523,751.
The means for supplying the imbricated formation, for example, comprise a pair of conveyor belts leading to the winding point essentially tangentially (e.g., to the zone of the lower zenith of the core or the roll under formation), on which conveyor belts the imbricated formation of articles is conveyed lying loosely. The winding tape is fed-in, for example, between the two conveyor belts such that the imbricated formation is guided to the winding point between the winding tape and the roll under formation. At the winding point, at which the supplied articles are taken over into the roll one after the other, the tensioned winding tape takes over the radial compression of the articles in the roll, this if so required somewhat assisted in the zone of the winding point by a corresponding pressure force exerted, for example, by the supplying device.
For adapting the winding device to the growing diameter of the roll under formation, either the supply means is correspondingly swivelled or else the axis of the roll core is correspondingly displaced. The winding drive, for example, acts on the roll core or on the periphery of the roll under formation in the zone of the winding tape.
For re-establishing the imbricated formation from a roll, i.e., for an unwinding process, the winding device is operated substantially in the opposite direction to the winding process, wherein the roll rotation is, for example, produced by actively pulling the winding tape off the roll.
It is found, that the rolls described above and their production and dissolution is less prone to problems, the smaller and more regular the thickness of the articles is, the less compressible the articles are and the less tightly the articles are arranged in the imbricated formation. In rolls made up of relatively thick, compressible and/or tightly imbricated printed products, the winding tape produces a constriction such that the products, at least in the outer layers of the roll under formation, bend outwards around the winding tape such that the roll has a greater circumference in the region of its two faces than in the central region, where it is held together by the winding tape. If, in addition, the products concerned are thicker on one side than on the other side, a dissymmetry is added to the constriction such that the two faces of the roll have different diameters.
The mentioned phenomenon can lead to problems due to the fact that they destabilise the roll and that the articles in the roll get damaged. Furthermore, as a result of the article deformation, the articles cannot assume a stable position in an imbricated formation re-produced from the roll. Problems may arise also on winding or unwinding because it becomes difficult to adapt the circumferential speed of a roll under formation or being unwound to the speed of a supply system or a conveying away system. The named problems are known in the printing field in particular for the winding of relatively thick printed products that are folded twice and of which in the roll, the second fold is aligned parallel to the roll axis such that unfolded product edges (smaller thickness) are lying on top of each other on the one roll face and first folds (greater thickness) are lying on top of one another on the other roll face. Products of this kind, for example, are twice folded newspapers or twice folded newspaper sections.
The invention sets itself the objective of improving method and device for producing rolls comprising a large number of flat articles, in such a manner, that the problems mentioned above occur less frequently and that therefore, also relatively thick, relatively compressible and/or irregular articles and in particular articles, which are thicker on one side, can be wound into rolls with better results, even when they are to be rolled in tight imbricated formations (small distances between adjacent articles).
In accordance with the present invention the flat articles in a roll under formation are, during the winding process, not only pressed against the roll core by the tensioned winding tape (central zone) and by their own stiffness (lateral zones), but they are temporarily subjected to an additional pressure force. During the winding process, the additional pressure force acts locally in a pressure zone on the periphery of the roll under formation and at a distance from the winding point. The pressure zone is substantially stationary and the additional pressure force comprises a component in the direction of the roll radius. The additional pressure force may, for example, be exerted over the whole width of the roll. Advantageously, however, the additional pressure force is restricted to lateral zones beside the winding tape reaching to the edge of roll face. Advantageously, the pressure zone is situated relative to the winding direction behind the winding point such that articles compressed by the additional pressure force reach the winding point soon afterwards to be covered by a further layer of articles.
It is found that, for the case of twice folded paper products, such as newspapers or newspaper sections, a temporary compression with an additional pressure force in the order of magnitude of some hundreds of Newtons (approximately 200 to 1000 N) is surprisingly effective. The additional pressure force is, for example, generated with the help of a passively rotating pressure roller pressed against the periphery of the roll under formation, the axis of the pressure roller being aligned parallel to the roll axis, and the pressure roller being arranged relative to the winding direction behind the winding point and at a distance from it. It is found that rolls wound with the additional pressure force according to the invention are wound more tightly and as a result are more stable. This is demonstrated, for example, by the fact that they flatten less when deposited standing on their periphery. It is also found, that rolls wound in this manner cause less problems on unwinding and also that the products from such rolls cause less problems during unwinding and during subsequent processing.
In rolls of folded printed products, the advantageous effect of the additional pressure force, which during the winding process acts on the outermost roll layer and through it also on layers located deeper in the roll, is probably at least in part attributable to an at least partially irreversible or at least not immediately reversible compression of the folded edges (in particular of the second fold) and compression (pressing out of air) of the products such that the products of a next roll layer are less deformed when first compressed by the winding tape on being taken over into the roll, than is the case without the additional pressure force.
The additional pressure force of the method in accordance with the invention is advantageous in particular for producing rolls, i.e. for winding processes. It can, however, be similarly used for unwinding operations.